Re: [PATCH v2 1/2] riscv: Add instruction dump to RISC-V splats

[Geert Uytterhoeven]

Hi Björn,

On Mon, Jan 16, 2023 at 8:41 AM Björn Töpel <bjorn@xxxxxxxxxx> wrote:
> From: Björn Töpel <bjorn@xxxxxxxxxxxx>
>
> Add instruction dump (Code:) output to RISC-V splats. Dump 16b
> parcels.
>
> An example:
>   Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>   Oops [#1]
>   Modules linked in:
>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.2.0-rc3-00302-g840ff44c571d-dirty #27
>   Hardware name: riscv-virtio,qemu (DT)
>   epc : kernel_init+0xc8/0x10e
>    ra : kernel_init+0x70/0x10e
>   epc : ffffffff80bd9a40 ra : ffffffff80bd99e8 sp : ff2000000060bec0
>    gp : ffffffff81730b28 tp : ff6000007ff00000 t0 : 7974697275636573
>    t1 : 0000000000000000 t2 : 3030303270393d6e s0 : ff2000000060bee0
>    s1 : ffffffff81732028 a0 : 0000000000000000 a1 : ff60000080dd1780
>    a2 : 0000000000000002 a3 : ffffffff8176a470 a4 : 0000000000000000
>    a5 : 000000000000000a a6 : 0000000000000081 a7 : ff60000080dd1780
>    s2 : 0000000000000000 s3 : 0000000000000000 s4 : 0000000000000000
>    s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
>    s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
>    s11: 0000000000000000 t3 : ffffffff81186018 t4 : 0000000000000022
>    t5 : 000000000000003d t6 : 0000000000000000
>   status: 0000000200000120 badaddr: 0000000000000000 cause: 000000000000000f
>   [<ffffffff80003528>] ret_from_exception+0x0/0x16
>   Code: 862a d179 608c a517 0069 0513 2be5 d0ef db2e 47a9 (c11c) a517
>   ---[ end trace 0000000000000000 ]---
>   Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>   SMP: stopping secondary CPUs
>   ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---
>
> Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxxxx>

Thanks for your patch!

> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -29,6 +29,27 @@ int show_unhandled_signals = 1;
>
>  static DEFINE_SPINLOCK(die_lock);
>
> +static void dump_kernel_instr(const char *loglvl, struct pt_regs *regs)
> +{
> +       char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
> +       unsigned long addr = regs->epc;

Given you never use this as an unsigned long, what about

    const u16 *insns = (u16 *)instruction_pointer(regs);

so you no longer need casts below?

> +       long bad;
> +       u16 val;
> +       int i;
> +
> +       for (i = -10; i < 2; i++) {
> +               bad = get_kernel_nofault(val, &((u16 *)addr)[i]);
> +               if (!bad) {
> +                       p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
> +               } else {
> +                       printk("%sCode: Unable to access instruction at 0x%lx.\n",

%px, so you can drop the cast to long below.

> +                              loglvl, (long)&((u16 *)addr)[i]);
> +                       return;
> +               }
> +       }
> +       printk("%sCode: %s\n", loglvl, str);
> +}
> +
>  void die(struct pt_regs *regs, const char *str)
>  {
>         static int die_counter;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds